From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,LOTS_OF_MONEY autolearn=ham autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,6482d0ae6dcb1b4c X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2002-10-20 19:17:31 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!logbridge.uoregon.edu!arclight.uoregon.edu!wn14feed!wn12feed!worldnet.att.net!bgtnsc05-news.ops.worldnet.att.net.POSTED!not-for-mail From: "David Thompson" Newsgroups: comp.lang.ada References: <3d9245da.259420486@news.cis.dfn.de> <3D933A6B.5000105@cogeco.ca> <8db3d6c8.0209270247.5bf07ae5@posting.google.com> <3D94D418.5010604@attbi.com> <9WZ5dN1lmUZv@eisner.encompasserve.org> Subject: Re: if file exist X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 5.00.2615.200 X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2615.200 Message-ID: <%sJs9.19905$1P1.1202599@bgtnsc05-news.ops.worldnet.att.net> Date: Mon, 21 Oct 2002 02:17:31 GMT NNTP-Posting-Host: 12.89.138.142 X-Complaints-To: abuse@worldnet.att.net X-Trace: bgtnsc05-news.ops.worldnet.att.net 1035166651 12.89.138.142 (Mon, 21 Oct 2002 02:17:31 GMT) NNTP-Posting-Date: Mon, 21 Oct 2002 02:17:31 GMT Organization: AT&T Worldnet Xref: archiver1.google.com comp.lang.ada:29968 Date: 2002-10-21T02:17:31+00:00 List-Id: Larry Kilgallen wrote : > In article , "David Thompson" writes: > > Mark Biggar wrote : ... > >> No, from a computer security point of view, this is exactly what is > >> wanted. A user should see absolutely no difference between "file does > >> not exist" and "you don't have permission to see the file". Otherwise, > >> you have introduced a covert information channel. > >> > > First this only matters if you want/need nondiscretionary controls. > > Non-discretionary controls, known as MAC for Mandatory Access Controls, > are when the direct data owner (e.g., file owner) does not have full > rights to control protection, for instance no right to disclose. > Yes, and not just the owner, but also other users who are authorized to read and/or write, if any. > The inability to tell whether an inaccessible file exists is _NOT_ > restricted to MAC situations. Under DAC (Dicretionary Access Controls) > the data owner may very well wish to restrict knowledge of file existence. > Whether the desire for non-disclosure comes from the data owner or some > higher authority has nothing to do with what characteristics are required > in order to avoid disclosing the presence of a file. But only MAC really needs to be concerned about covert channels, since a DAC-authorized user is permitted to use open channels. AFAICT it is rare(r?) in DAC situations to care about disclosing existence, only contents, but if it is, it is common (and I am assuming possible) to put the file in a directory which is restricted against unauthorized probing for member's names and existence. -- - David.Thompson 1 now at worldnet.att.net